水利水电工程毕业设计英文翻译,混凝土重力坝

1、Concrete Gravity DamThe type of dam selected for a site depends principally on topographic, geologic,hydrologic, and climatic conditions. Where more than one type can be built, alternative economic estimates are prepared and selection is based on economica considerations.Safety and performance are p

2、rimary requirements, but construction time and materials often affect economic comparisons.Dam ClassificationDams are classified according to construction materials such as concrete or earth. Concrete dams are further classified as gravity, arch, buttress, or a combination of these. Earthfill dams a

3、re gravity dams built of either earth or rock materials, with particular provisions for spillways and seepage control.A concrete gravity dam depends on its own weight for structural stability. The dam may be straight or slightly curved, with the water load transmitted through the dam to the foundati

4、on material. Ordinarily, gravity dams have a base width of 0.7 to 0.9 the height of the dam. Solid rock provides the best foundation condition. However, many small concrete dams are built on previous or soft foundations and perform satisfactorily. A concrete gravity dam is well suited for use with a

5、n overflow spillway crest. Because of this advantage, it is often combined with an earthfill dam in wide flood plain sites.Arch dams are well suited to narrow V- or U-shaped canyons. Canyon walls must be of rock suitable for carrying the transmitted water load to the sides of the canyon by arch acti

6、on. Arch sections carry the greatest part of the load; vertical elements carry sufficient load through cantilever action to produce cantilever deflections equal to arch deflections. Ordinarily, the crest length-to-height ratio should be less than 5, although greater ratios have been used. Generally,

7、 the base width of modern arch dams is 0.1 to 0.3 the height of the impounded water. A spillway may be designed into the crest of an arch dam.Multiple arches similarly transmit loads to the abutment or ends of the arch. This type of dam is suited to wider valleys. The main thrust and radial shears a

8、re transmitted to massive buttresses and then into the foundation material.Buttress dams include flat-slab, multiple-arch, roundhead-buttress, and multiple-dome types. The buttress dam adapts to all site locations. Downstream face slabs and aprons are used for overflow spillways similar to gravity d

9、am spillways. Inclined sliding gates or light-weight low-head gates control the flow.The water loads are transmitted to the foundation by two systems of load-carrying members. The flat slabs, arches, or domes support the direct water load. The face slabs are supported by vertical buttresses. In most

10、 flat-slab buttress dams, steel reinforcement is used to carry the tension forces developed in the face slabs and buttress supports. Massive-head buttresses eliminate most tension forces and steel is not necessary.Combiantion designs may utilize one or more of the previously mentioned types of dams.

11、 For example, studies may indicate that an earthfill dam with a center concrete gravity overflow spillway section is the most economial in a wide, flat valley. Other design conditions may dictate a multiple-arch and buttress dam section or a buttress and gravity dam combination.Site ExplorationThe d

12、am location is determined by the project s functions. The exact site within the general location must be determined by careful project consideration and systematic studies.In preliminary studies, two primary factors must be determined-the topography at the site and characteristics of the foundation

13、materials. The first choice of the type of dam is based primarily on these two factors. However, the final choice will usually be controlled by construction cost if other site factors are also considered.Asite exploration requires the preparation of an accurate topographic map for each possible site

14、 in the general location. The scale of the maps should be large enough for layout. Exploration primarily determines the conditions that make sites usable or unusable.From the site explorations, tentative sketches can be made of the dam location and project features such as power plants. Physical fea

15、tures at the site must be ascertained in order to make a sketch of the dam and determine the position of materials and work plant during construction. Other factors that may affect dam selection are roadways,fishways, locks, and log passages.TopographyTopography often determines the type of dam. For

16、 example, a narrow V-shaped channel may dictate an arch dam. The topography indicates surface characteristics of the valley and the relation of the contours to the various requirements of the structure. Soundness of the rock surface must be included in the topographic study.In a location study, one

17、should select the best position for the dam. An accurate sketch of the dam and how it fits into the topographic features of the valley are often sufficient to permit initial cost estimates. The tentative location of the other dam features should be included in this sketch since items such as spillwa

18、ys can influence the type and location of the dam.Topographic maps can be made from aerial surveys and subsequent contour plotting or they can be obtained from governmental agencies. The topographic survey should be correlated with the site exploration to ensure accuracy. Topographic maps give only

19、the surface profile at the site. Further geological and foundation analyses are necessary for a final determination of dam feasibility.Foundation and Geological InvestigationFoundation and geological conditions determine the factors that support the weight of the dam. The foundation materials limit

20、the type of dam to a great extent, although such limitations can be compensated for in design.Initial exploration may consist of a few core holes drilled along the tentatively selected site location. Their analysis in relation to the general geology of the area often rules out certain sites as unfea

21、sible, particularly as dam height increases. Once the number of possible site locations has been narrowed down, more detailed geological investiagtions should be considered.The location of all faults, contacts, zones of permeability, fissures, and other underground conditions must be accurately defi

22、ned. The probable required excavation depth at all points should be derived from the core drill analysis. Extensive drilling into rock formations isn' t necessary for small dams. However, as dam height and safety requirements increase, investigations should be increased in depth and number. If f

23、oundation materials are soft, extensive investigations should determine their depth,permeability, and bearing capacity. It is not always necessary or possible to put a concrete dam on solid rock.The different foundations commonly encountered for dam construction are: (1)solid rock foundations, (2) g

24、ravel foundations, (3) silt or fine sand foundations, (4) clay foundations, and (5) nonuniform foundation materials. Small dams on soft foundation ( item 2 through item 5 ) present some additonal design problems such as settlement, prevention of piping, excessive percolation, and protection of found

25、ation from downstream toe erosion. These conditions are above the normal design forces of a concrete dam on a rock foundation. The same problems also exist for earth dams.Geological formations can often be pictured in cross-section by a qualified geologist if he has certain core drill holes upon whi

26、ch to base his overall concept of the geology. However, the plans and specifications should not contain this overall geological concept. Only the logs of the core drill holes should be included for the contractor, s estimates. However, the geological picture of the underlying formations is a great a

27、id in evaluating the dam safety. The appendix consists of excerpts from a geologic report for the site used in the design examples.HydrologyHydrology studies are necessaryto estimate diversion requirements during construction, to establish frequency of use of emergency spillways in conjunction with

28、outlets or spillways, to determine peak discharge estimates for diversion dams, and to provide the basis for power generation. Hydrologic studies are complex; however, simplified procedures may be used for small dams if certain conservative estimates are made to ensure structural safety.Formulas are

29、 only a guide to preliminary plans and design computations. The empirical equations provide only peak discharge estimates. However, the designer is more interested in the runoff volume associated with discharge and the time distribution of the flow. With these data, the designer knows both the peak

30、discharge and the total inflow into the reservoir area. This provides a basis for making reliable diversion estimates for irrigation projects, water supply, or power generation.A reliable study of hydrology enables the designer to select the proper spillway capacity to ensure safety. The importance

31、of a safe spillway cannot be overemphasized.Insufficient spillways have caused failures of dams. Adequate spillway capacity is of paramount importance for earthfill and rockfill dams. Concrete dams may be able to withstand moderate overtopping.Spillways release excess water that cannot be retained i

32、n the storage space of the reservoir. In the preliminary site exploration, the designer must consider spillway size and location. Site conditions greatly influence the selection of location, type, and components of a spillway. The design flows that the spillway must carry without endangering the dam

33、 are equally important. Therefore, study of streamflow is just as critical as the foundation and geological studies of the site.附录2外文翻译混凝土重力坝一个坝址的坝型选择，主要取决于地形、地质、水文和气候条件。对于那些 有几种坝型可建造的地方，则要进行经济比较估算，并根据经济条件来做选择。 安全和运行性能是基本的要求，但是施工时间和材料也常会影响到经济比较。坝的分类坝可按照建筑材料（像混凝土或土）来分类。混凝土坝又进一步分为重力坝、 拱坝、支墩坝或这些类型的组合。土

34、坝则是用土或岩石材料建造的重力式坝，并 要设有溢洪道和控制渗漏的特殊设施。混凝土重力坝依靠本身的重量来维持结构稳定。水荷载经过坝传递到坝基，坝可以是直的或稍呈曲线型。通常，重力坝的底宽是高度的0.70.9。坚硬岩石是 最好的地基条件，不过，许多小混凝土坝都建筑在透水或软质地基上， 而且运行 良好。混凝土重力坝最适合于在坝顶设置溢流式溢洪堰， 由于这一优点，它经常 和土坝结合使用在宽阔的洪泛平原坝址上。上述一种或几种坝型可以组合使用。 例如，方案研究可能表明，在宽阔而平 坦的河谷内，一种在中间段设置混凝土重力式溢洪道的土坝是最经济的。 在其它 设计情况下，也可能采用连拱和支墩坝段或支墩和重力坝的

35、组合。坝址查勘坝的位置是由工程的任务决定。在大致选定的位置（即坝址段）范围内，正 确的坝址则必须经过仔细的规划考虑和系统的研究后决定。在初步研究时，必须确定两个基本因素：即坝址的地形和地基材料的特性。 第一次选择坝型主要是根据这两个因素。但是，如果坝址的其它因素也都考虑之 后，则最终的选择常将由建设费用决定。坝址查勘需要对坝址段内每个可能采用的坝址准备好一张准确的地形图。图的比例尺应大到满足布置的需要。查勘任务主要是查明坝址适用或不适用的一些 条件。通过坝址查勘，就能绘制坝的位置和工程附属建筑物如发电厂房的示意图。 坝址处的自然条件必须查明，以便绘出坝的示意图并确定料场和施工期辅助企业 的位置。其它影响选坝的因素有道路、鱼道、船闸和筏道等。地形地形常常决定坝型。例如，一个狭窄 V形河槽可选用拱坝。地形显示出河 谷的表面特征以及等高线和结构各种要求之间的关系。岩石表面的坚固完整情 况，必须包括在地形研究之类。在坝址研究中，应该为坝选择最好的位置。一张精确的坝体轮廓图，同时表 示出坝如何与河谷地形特征相适应的情况， 往往就足够供基建费的估算使用。坝 的其他附属建筑物的设想位置，也要包括在轮廓图内，因为诸如溢洪道等项目会 影响坝型和坝址的选择。地形图可以从航空测量和随后描绘的等高线制作，或者可以从政府机关取 得。地形测量应和坝址查勘相结合，以确保其正确性